The present invention relates to a quantum dot semiconductor device and a method for fabricating the quantum semiconductor device, more specifically a quantum semiconductor device having a quantum dot and a method for fabricating the quantum semiconductor device.
Recently, semiconductor devices, such as MOS transistors, etc., are rapidly increasingly micronized.
The micronization of semiconductor devices, such as MOS transistors, etc., is limited. In MOS transistors, for example, when the gate length is too short, the normal switching is impossible.
Then, as a device which can realize further micronization, single electron devices are proposed. Single electron devices have small power consumption and are much noted in terms of decreasing the power consumption.
For example, Patent Reference 1 proposes a single electron transistor comprising a first gate electrode which is formed on a semiconductor of a two-dimensional electron structure and which is divided in a plurality of parts, and a second gate electrode in a region enclosed by the first gate electrode with an insulation film formed there between. In such single electron transistor, an electron confined region is formed due to a depletion layer generated by applying a voltage to the first gate electrode. By applying a voltage to the second electrode, the single electron transition can be controlled.
Patent Reference 2 proposes a single electron transistor comprising quantum wires.
Patent Reference 3 proposes a single electron transistor comprising quantum boxes formed in concavities formed in a semiconductor surfaces.
However, in the proposed single electron devices described above, electrons are confined in relatively large region, which makes it impossible to obtain discrete energy levels, and what are obtained are only classic effects, such as Coulomb blockade. Furthermore, the Coulomb blockade cannot be produced without setting the temperature to be sufficiently low.
To produce Coulomb blockade at relative high temperatures it is necessary to form fine quantum dots. In the fine quantum dots, discrete energy levels can be obtained, which permits Coulomb blockade to take place at relatively high temperatures. To produce Coulomb blockade at the room temperature, for example, the size of the quantum dots must be below about 10 nm.
Patent Reference 4 proposes a single electron device comprising fine quantum dots formed in the side wall of a step formed in a substrate, and a gate electrode formed, covering the quantum dots. In Patent Reference 4, fine quantum dots are used, which permits the device to operate at relatively high temperatures.
Following references disclose the background art of the present invention.
[Patent Reference 1]
Specification of Japanese Patent Application Unexamined Publication No. Hei 6-196720
[Patent Reference 2]
Specification of Japanese Patent Application Unexamined Publication No. 2002-518851
[Patent Reference 3]
Specification of Japanese Patent Application Unexamined Publication No. Hei 10-303408
[Patent Reference 4]
Specification of Japanese Patent Application Unexamined Publication No. Hei 11-150261
[Patent Reference 5]
Specification of Japanese Patent Application Unexamined Publication No. Hei 5-211342
[Patent Reference 6]
Specification of Japanese Patent Application Unexamined Publication No. 2000-91451
[Patent Reference 7]
Specification of Japanese Patent Application Unexamined Publication No. 2001-7315
[Non-Patent Reference 1]
Keyser et al., Appl. Phys. Lett. 76, 457 (2000)
[Non-Patent Reference 2]
T. Fujisawa et al., Phys. Rev. B63, 081304R.(2001)
However, the single electron device proposed in Patent Reference 4 has too complicated operation to be practically applied.